This invention relates to a supporting sturcture for a steering apparatus of the rack and pinion type.
As a conventional supporting structure for a steering apparatus of the rack and pinion type, for example, there is known a supporting structure such as shown in FIGS. 1 and 2. In the drawings, a rack axle supporting member R is constituted by a gear housing 1 and a rack tube 2. The rack tube 2 is connected to one end of the through-hole of the housing 1. A rack axle 3 is axially movably supported through a rack bush 5 in the rack axle supporting member R. Ball sockets 7 are threadably attached to the opposite ends of the rack axle 3, respectively. Two balls studs 9 which are respectively mounted to one end of each of two steering rods 8 are inserted into the ball sockets 7 respectively, thereby movably coupling the steering rods 8 to the opposite ends of the rack axle 3. A knuckle arm (not shown) is connected through a ball joint (not shown) to the other end of each of the steering rods 8. Furthermore, right and left road wheels for steering (not shown) are individually connected to the knuckle arms respectively. Rack boots 10 are provided on the opposite ends of the rack axle 3.
The gear housing 1 includes a pinion 4 to be interconnected to a steering shaft (not shown). The gear teeth of this pinion 4 engage a rack 3a of the rack axle 3 in the gear housing 1. The pinion 4 rotates with the rotation of the steering wheel to be attached to the upper end of the steering shaft. Thus, the rack axle 3 having the rack 3a adapted to engage the gear teeth of the pinion 4 moves relatively axially with respect to the rack axle supporting member R. As a result, the knuckle arms are rotated by means of the steering rods 8 which move along with the rack axle 3, thereby revolving the right and left road wheels for steering (not shown) of the vehicle.
The rack axle supporting member R is supported through mounting insulators 11 and 12 on the vehicle body (not shown) by means of clamping brackets 13 and 14. In other words, the ring-shaped mounting insulators 11 and 12 are attached to the outer peripheries of the gear housing 1 and rack tube 2. The mounting insulators 11 and 12 are mounted to predetermined locations in a vehicle body member 15 with the fitting portions of the mounting insulators coming into engagement therewith, for example, as shown in FIG. 2. The clamping brackets 13 and 14 are positioned around the mounting insulators 11 and 12 to sandwich the mounting insulators 11 and 12 respectively. Bolts 16 are inserted into the vehicle body member 15 through the clamping brackets 13 and 14 with their head portions being in threaded engagement with the member 15. Then, the bolts 16 are wrenched to elastically support the rack axle supporting member R onto the vehicle body through the mounting insulators 11 and 12.
In FIGS. 1 and 2, a protrusion 1a for positioning is formed in the gear housing 1, and an opening 13a adapted to receive this protrusion 1a therethrough is formed in the clamping bracket 13. A portion of the mounting insulator 11 and the protrusion 1a are inserted into this opening 13a, thereby restricting the circumferential rotation of the rack axle supporting member R.
However, in such a conventional supporting structure of the steering apparatus of the rack and pinion type, the mounting insulators 11 and 12 are interposed in a compressed condition between the rack axle supporting member R and the clamping brackets 13 and 14 to support the supporting member R onto the vehicle body. Therefore, the compression of the mounting insulators 11 and 12 changes according to differences in dimensional accuracy of each part such as the gear housing 1, clamping brackets 13 and 14, or the like, and according to the difference in the clamping forces of the respective bolts 16, so that the elastic constant of the mounting insulators 11 and 12 will largely vary. Moreover, since the rack axle supporting member R is elastically supported onto the vehicle body by means of the spring or elastic forces of the mounting insulators 11 and 12, when the rigidity of the mounting insulators 11 and 12 is high, the elastic constant of the mounting insulators 11 and 12 in the axial direction of the rack axle becomes large, causing shimmy to easily occur. On the other hand, there is also a problem that when the rigidity of the mounting insulators 11 and 12 is low, the durability of the mounting insulators 11 and 12 is reduced, even though it is effective to suppress the shimmy and to improve the maneuver stability during high-speed driving.